The inventors have proposed ceramics prepared by sintering a matrix of titanium diboride with the addition of zirconium dioxide (ZrO.sub.2) (Japanese Patent Publication No. 7668 of 1984) and sintered ceramics prepared with the addition of cubic carbide (Japanese Patent Publication No. 7669 of 1984). These ceramics are suited for use as abrasion-resistant materials that are required to have considerable toughness. With the marked progress of industry in recent years, there are increasing demands for ceramics that are easier to sinter and have more improved properties.
Therefore, the inventors are continuing studies on the further improvement of the properties of metallic boride-zirconium oxide-metallic carbide-based ceramics.
When zirconium dioxide is added for the improvement of toughness, in particular, the zirconium dioxide stabilizer used together causes thermal deterioration. As such, composite ceramics sintered with zirconium dioxide stabilized by yttrium oxide (Y.sub.2 O.sub.3) or other similar stabilizer have been used only for services involving not much higher temperatures than the room temperature.